Based on some of the questions asked at the Genius Table at the last MacGroup meeting, it sounds like people are a bit confused about iCloud and whether or not they should move from MobileMe. Since that trip is one way if you take it (no going back), you best be sure that’s what you want to do before you take the plunge.
First off, if you want to sync your calendar and contacts with your iDevice (iPhone, iPod Touch, or iPad) on iOS5, and you aren’t running the most current version of Lion (10.7.2), then you should not move to iCloud. Stick with MobileMe. There is a work-around for your calendars if you are on Snow Leopard, and you can always use any IMAP client for mail, but your contacts will not sync via iCloud without Lion.
If you want to use a mail client besides Apple Mail, just use the information in this Apple Knowledge Base article to set up your mail client. You must use a client that understand IMAP – no more POP mail (and that’s actually a good thing).
If you want to sync calendars with a Snow Leopard (10.6) machine, you can go into iCal preferences and then Accounts to create a new CalDAV account. Click the plus sign at the bottom for a new account, change the type from Automatic to CalDAV, and fill in your email@example.com username and password (make sure you use the “@.me” after your name). For the server, use p02-caldav.icloud.com. You may get a dialog box like this one:
Select the iCloud server, click “Create,” and you’re all set. Leopard (10.5) supposedly supports CalDAV, but I couldn’t make it work.
A better alternative might be to switch to Google for your contacts and calendar syncing. Leopard and Snow Leopard both support this natively (Leopard with 10.5.3, and all versions of Snow Leopard).
Don’t forget that MobileMe will continue to work until next June. So you don’t have to rush into anything. Maybe you’re planning an upgrade to Lion in a few months. If so, you might just want to sit tight with MobileMe until then.